Apparatus and method for registration of shadow masked thin-film patterns

ABSTRACT

An apparatus and method for registration or alignment of thin film structure patterns on a substrate formed with the use of an apertured mask in a vacuum deposition system. On particular the alignment apparatus is comprised of a mask holder assembly, which supports the apertured mask, and a substrate carrier which engages with the holder assembly. Upon placing the engaged alignment apparatus in a a deposition chamber, a magnet is positioned adjacent the holder assembly in order to formly hold the apertured mask against a substrate prior to vacuum to deposition. Upon depositing the pattern material, the magnet and holder assembly are disengaged, resulting in a pattern of thin film structures remaining on the substrate. The present invention is effective for remotely operating automatic masking systems where there is a need to eliminate the need for breaking vacuum in a deposition system.

This is a divisional of co-pending application Ser. No. 790,695 filed onOct. 23, 1985 now U.S. Pat. No. 4,746,548.

CROSS-REFERENCE TO CO-PENDING APPLICATIONS

In co-pending application Ser. No. 790,590, now U.S. Pat. No. 4,715,940,("Mask for Patterning Electrode Structures in Thin-Film ElDevices"--Robert Boudreau), there is defined a mask structure and amethod of fabricating electrode structures for a thin-film EL devicethat utilizes such a mask structure.

In co-pending application Ser. No. 790,589, now U.S. Pat. No. 4,615,781,("Mask Assembly Having Mask Stress Relieving Feature"--Robert Boudreau),there is defined a mask assembly that provides support for a shadow maskwhile eliminating mask wrinkling during patterning of thin-filmstructures.

Both of the above applications are filed concurrently herewith and areassigned to the same assignee as the instant invention.

TECHNICAL FIELD

The present invention relates in general to the deposition of depositingthin-film structures, and particularly to an apparatus and a method forthin-film structure patterns on a substrate for a thin-film displaydevice.

BACKGROUND OF THE INVENTION

Thin-film display panels (such as LCD or electroluminescent) have beenknown to be very useful for displaying information as the thin-filmstructures including the cross electrodes and contact pads, can bedeposited on a glass substrate thereby providing a matrix display panelcapable of being selectively energized to activate individual pixelsthereon. One of the problems encountered in the manufacture of thin filmdisplay panels is the development of processes that pattern the thinfilm electrode structures while in an in-line deposition system.

Most thin-film devices have had their thin-film structures patternedeither by a wet process known as photolithography or by shadow masking.Photolithography is very similar to processes used to developphotographs in that the deposit to be patterned is coated withlight-sensitive material, which is then exposed to a negative orpositive pattern and then developed and later stripped in variouscorrosive developing solutions. The disadvantages of this method is thatit is slow and labor intensive, and involves many steps, each onesubject to failure or possible contamination of the thin-film device.

With respect to the use of shadow masking to deposit thin-filmstructures, reference is made to U.S. Pat. No. 4,335,161 to Fang C. Luo,entitled "Thin-Film Transistors, Thin-Film Transistor Arrays and aProcess for Preparing the Same". In summary, the Luo patent appears todisclose a method of preparing a thin-film transistor or an array ofthin-film transistors by depositing in vacuum the different componentsthrough a single apertured mask, wherein the apertured mask is moved inpredetermined pattern for the deposition of each of the components. InLuo, once the deposition of the different structures is complete, theassembly that is formed is then removed from the vacuum and thefabrication completed by techniques such as photolithography.

As in Luo, shadow masking is usually performed over small substrateswith stiff masks that are manually clamped to ensure even contact with aparticular substrate. This is a relatively slow process and usuallyrequires breaking vacuum in the deposition chamber, resulting in somethin-film contamination. When depositing through a large area mask, itis common that the substrate is not perfectly flat or not level withrespect to its surrounding substrate holder. The present inventionaddresses the problem arising from the difficulties of remote automatichandling of large area shadow masks in an in-line deposition system.

With respect to the use of photolithography, thin-film patterns havetypically been aligned to the substrate and each other by optical meansand the substrate is moved manually into position with the aid of amicromanipulator or an optical scanner which provides information to acomputer which performs a similar function. The aligned substrate isthen exposed and wet processed to achieve the desired pattern. Incontrast, most shadow masking processes are aligned manually by droppingthe masks over pins located on a substrate carrier. Therefore, anapparatus which is effective for remotely operating automatic maskingsystems where there is a need to eliminate the need for breaking vacuum,which would contaminate deposit of thin films, would be considered anadvancement in the art.

DISCLOSURE OF THE INVENTION

It is therefore a primary object of this invention to enhance the art ofthin-film structure deposition, and particularly the art involvingthin-film display panels.

It is another object of this invention to provide an apparatus foraiding in the alignment of thin-film structures patterned in thin-filmdevices.

Still another object of the invention is to provide a method of aligningthin-film structures that are to be patterned on the substrate throughthe use of a vacuum deposition process.

A further object of the present invention is to provide an apparatus anda method for automatically aligning thin-film structures to be patternedon a substrate while in an in-line deposition system.

In accordance with one aspect of this invention, there is provided anapparatus for the alignment of thin-film structure patterns on asubstrate formed with the use of an apertured mask in a vacuumdeposition system. The apparatus comprises a mask frame and a maskassembly affixed to the mask frame, the mask assembly including theapertured mask and mask alignment apertures which are disposed on eitherside of the mask. A mask holder frame is positioned adjacent the maskassembly and is affixed to the mask frame to form a mask holderassembly, the mask holder assembly having primary datum pins affixedthereto and protruding from the side of the holder assembly oppositesaid mask assembly. Finally, the alignment apparatus includes asubstrate carrier, having a substrate supported therein, positionedadjacent and in operative contact with mask holder assembly; thesubstrate carrier has primary datum apertures, that engage with theprimary pins of the mask holder assembly, which are disposed on theperiphery of the carrier. In addition, the carrier has secondary datumpins protruding therefrom that engage with the mask alignment aperturesof the mask assembly.

In accordance with another aspect of this invention, there is provided amethod of aligning thin-film structure patterns on a substrate formedwith the use of an apertured mask in a vacuum deposition system. Thealignment method comprises the steps of positioning a mask holderassembly within a deposition chamber, such holder assembly having theapertured mask as part thereof and having means for engaging a substratecarrier. A substrate carrier is then positioned within the depositionchamber spaced from the mask holder assembly, the carrier having thesubstrate supported therein and having means for aligning the aperturedmask with the substrate. The mask holder assembly is then engaged withthe substrate carrier such that they are in operative contact. A magnetis then positioned in the deposition chamber adjacent the side of thesubstrate carrier opposite the mask holder assembly such that theapertured mask is held in operative contact with the substrate.Furthermore, a thin-film structure material is then vacuum-depositedthrough the apertured mask and the magnet is then removed from thesubstrate carrier and the mask holder assembly disengaged from thesubstrate carrier, thereby resulting in the formation of thin-filmstructures on the substrate.

In accordance with still another aspect of this invention, there isprovided a method of aligning thin-film structure patterns on asubstrate formed with the use of an apertured mask in a vacuumdeposition system. The alignment method comprises the steps of providinga mask frame and affixing a mask assembly to the mask frame, the maskassembly including the apertured mask and mask alignment apertures thatare disposed on either side of the mask. A mask holder frame is affixedthrough the mask assembly to the mask frame to form a mask holderassembly, the mask holder assembly having primary datum pins affixedtherethrough and protruding from the side opposite the mask assembly.The mask holder assembly is then positioned in a vacuum depositionchamber while a substrate carrier is then positioned in the depositionchamber spaced from the mask holder assembly. The carrier has thesubstrate supported therein and has primary datum apertures disposedabout the periphery of the carrier; the carrier has secondary datum pinsprotruding from the side adjacent the mask holder assembly. The maskholder assembly is then engaged with the substrate carrier such that theprimary datum pins are first engaged with the primary apertures of thecarrier while the secondary datum pins are subsequently engaged with themask alignment apertures of the mask assembly. Next, a magnet ispositioned in the deposition chamber adjacent the side of the carrieropposite the mask holder assembly such that the apertured mask is heldin operative contact with the substrate; a thin-film structure materialis then vacuum-deposited through the apertured mask. Finally, the magnetis removed from the substrate carrier and the mask holder assembly isdisengaged from the substrate carrier thereby resulting in the formationof thin-film structures on the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of an embodiment of the apparatus foraligning an apertured mask against a substrate, and

FIG. 2 illustrates an example of the alignment apparatus of FIG. 1within a deposition chamber that aids in describing the automaticaligning procedure.

BEST MODE FOR CARRYING OUT THE INVENTION

For a better understanding of the present invention, together with otherand further objects, advantages and capabilities thereof, reference ismade to the following disclosure and appended claims in connection withthe above-described drawings.

With particular attention to FIG. 1, there is illustrated a maskalignment or registration apparatus for ultimately aligning an aperturedmask to a glass substrate on which thin-film structures are to bedeposited. Alignment apparatus 10 is primarily comprised of a maskholder 12 and a substrate carrier 30, which supports (in this case) twosubstrates. In particular, mask holder assembly 12 is comprised of amask frame 14, a mask assembly 20 and a mask holder frame 26. In thisparticular embodiment mask frame 14 is substantially rectangular inshape and has a frame center support 16, which supports one set ofspring forks 18 that aid in engaging mask assembly 20 with substratecarrier 30, and has mask frame pins 17 (see FIG. 1). Mask holder frame26 also has pins 27 located about its periphery (e.g. top and bottom)for allowing mask frame 14 to be affixed thereon.

Mask assembly 20 has mounting holes 21, for mounting mask assembly 20 tomask frame pins 17, and supports an apertured mask 22 which aids indepositing thin-film structures on a glass substrate. Mask assembly 20also has mask alignment apertures 24 disposed on either side ofapertured mask 22. In addition, mask holder frame 26 has primary datumpins 28 affixed thereto and protruding from the side opposite maskassembly 20. As will be described in detail later in the Specification,primary datum pins 28 serve to engage mask holder assembly 12 withsubstrate carrier 30.

Referring again to FIG. 1. In this particular embodiment substratecarrier 30 is illustrated having at least two substrates 32 supportedtherein. Substrate carrier 30 is also substantially rectangular in shapeand has primary apertures 34 disposed about its periphery for engagingthe primary datum pins 28 of mask holder assembly 12. Primary apertures34 in this case are two in number and are typically named alignment orregistration holes for the purpose of aligning mask holder assembly 12,containing mask assembly 20 with substrates 32 of substrate carrier 30.The present invention operates on the basis of a primary and secondarydatum reference locations. The primary datum reference locatum isachieved when substrate carrier 30 is positioned adjacent and inoperative contact with mask holder assembly 12 such that primary datumapertures 34 will engage with primary datum pins 28. Substrate carrier30 also has a series of secondary datum pins 36 protruding therefromthat are disposed on the carrier side facing mask holder assembly 12.Secondary datum pins 36 will ultimately engage with secondary maskalignment apertures 24 of mask assembly 20. This engagement will nudgeapertured mask 22 into the higher accuracy secondary datum referencelocation (i.e. pins 36 and apertures 24) in order to properly alignapertured mask 22 with one of the substrates 32.

Spring forks 18 of mask frame 14 are considered means for aiding theengagement of mask assembly 20 with secondary datum pins 36 of substratecarrier 30. The spring forks are located substantially within andcoplanar with mask frame 14. A spring fork (i.e. 18) is included foreach of the secondary datum (i.e. 36) pins and are in operative contactwith mask assembly 20 while being aligned with mask alignment apertures24. In addition, apertured mask 22 is structurally relieved from maskassembly 20, which is rigidly attached within mask holder assembly 12,such that the mask is capable of being in operative contact with thesubstrate of substrate carrier 30. Mask alignment apertures 24 of maskassembly 20 include a hole and slot that engage with secondary pins 36of substrate carrier 30, as illustrated in FIG. 1, and complete thesecondary datum reference. As will be described in further detail inFIG. 2 and later in the Specification, alignment apparatus 10 furtherincludes a magnet 56 disposed adjacent and in operative contact withsubstrate carrier 30. Magnet 56 is disposed on the side of carrier 30opposite mask holder frame 26. Apertured mask 22, in this particularembodiment, can be designed for patterning electrode structures orelectrode pad contacts, but is not limited to such structures.

The apparatus described in this invention is most effective for remotelyoperated automatic masking systems where there is a need to eliminatethe breaking of vacuum which can contaminate the deposited thin-films.The invention provides a final secondary "short cut" datum registrationor alignment system eliminating tolerance build-up caused by chainedinterregistration of many separate parts by leaping over theseregistrations and creating a new, independent datum. Without the finalsecondary "short cut" datum registration afforded by this invention,registration would be through a series of datum mask holder pins,carrier bushings, tooling and glass holders. Even with a 0.001 inchtolerance for each machined part, the total tolerance would be greaterthan 0.005 inch and unacceptable towards making the patterns registerfor electrical connection off of a glass display substrate. Furthermore,the method for providing the final registration must be compatible withmechanical shadow masking to prevent blurs and defects in the resultingpatterns.

We have discovered that our present mask design allows enough forcedmovement of apertured mask 22 about its primary datum reference locationthrough a crude series of chained datums, that a secondary independentdatum can be used to make a more precise final registration of aperturedmask 22. The secondary independent datum, in this case secondary datumpins 36 and mask alignment aperatures 24, brings the patternregistration within the difficult tolerance needed to make a thin-filmstructure for a thin-film device. In FIG. 1 the location of the largeprimary chained datum registration pins 28 register mask assembly 12 tosubstrate carrier 30. The location of the much smaller secondary datumpins help register apertured mask 22 to substrate 32 with highprecision. This invention requires the less accurate chainedregistration system (i.e., primary datum pins 28 and primary apertures34) to get tolerances within a certain range to allow the secondarydatum system of the invention to engage and take effect.

A typical operation of the alignment apparatus' primary and secondarydatum reference system consists of ultimately locating mask assembly 20over secondary datum pins 36, by first engaging mask holder assembly 12with the less accurate, chained primary datum of mask frame 14 andsubstrate carrier 30. As mask holder assembly 12 reaches the end of itsprimary engagement stroke, mask assembly 20 begins to push maskalignment apertures 24 over the shorter length secondary datum pins 36.This engagement nudges the apertured mask 22 into the higher accuracysecondary datum reference location. Spring forks 18, mounted on andabout mask frame 14, aid in the engagement of alignment apertures 24with secondary pins 36. The spring forks press on mask assembly 20 onlyat the secondary pin locations so that friction does not inhibit lateralmovement of mask assembly 20 which would prevent it from aligning withthe pin position. Also, pressing at only the pin locations reduces maskstress, which can blur the mask pattern during the subsequent depositionstep. After mask assembly 20 is neatly engaged on secondary pins 36, ahold-down system such as magnet 56 brings mask 22 tight against glasssubstrate 32. Secondary registration or alignment is best performed byusing specially shaped apertures 24: a hole on one side of mask 22 and aslot on the other side so that secondary pins 36, utilizing these holes,do not bind with each other. Binding of the secondary datums with theprimary datums does not occur because the alignment error between theseparate datums is less than the flexible movement of mask 22.

Referring now to FIG. 2, there is illustrated alignment apparatus 10inside a vacuum deposition chamber 50 along with magnet 56 andsputtering apparatus 52. FIG. 2 illustrates a portion of a depositionsystem which may either be from an in-line or from a batch process typesystem. Sputtering apparatus 52 also has a layer of deposition material54 thereon which will be deposited through apertured mask 22 onto one ofthe substrates of substrate carrier 30.

The following will be a description of the method of aligning thin-filmstructure patterns on a substrate formed with the use of an aperturedmask in a vacuum deposition system. With the aid of FIG. 2, the methodcomprises the steps of positioning a mask holder assembly 12 within adeposition chamber 50, mask holder assembly 12 having apertured mask 22as part thereof and having means for engaging substrate carrier 30. Asubstrate carrier 30 is then positioned within deposition chamber 50spaced from mask holder assembly 12, carrier 30 having a substratesupported therein and having means for aligning apertured mask 22 withthe substrate. Next, mask holder assembly 12 is engaged with substratecarrier 30 such that they are in operative contact. A magnet 56 is thenpositioned in the deposition chamber adjacent the side of substratecarrier 30 opposite mask holder assembly 12 such that apertured mask 22is held in operative contact with the substrate. Thin-film structurematerial 54 is then vacuum-deposited through apertured mask 22. Finally,magnet 56 is removed from substrate carrier 30 and mask holder assembly12 is disengaged from carrier 30, thereby resulting in the formation ofthin-film structures on the substrate.

As described earlier, mask holder assembly 12 is comprised of mask frame14, mask assembly affixed to mask frame 14 and a mask holder frame 26that is affixed through mask assembly 20 to mask frame 14. In the methoddescribed, means for engaging substrate carrier 30 includes primarydatum pins 28 affixed through and protruding from mask holder assembly12 on the side opposite mask assembly 20. Substrate carrier 30 hasprimary apertures 34 disposed about the periphery for engaging primarydatum pins 28. All of the steps of the method described in aligning thethin-film structure patterns on the substrate can be performedautomatically in an in-line deposition system. The step ofvacuum-depositing includes sputtering, vapor deposition, or chemicalvapor deposition.

This invention can be varied in a number of ways, but the basicoperation of prealignment with a primary datum, (i.e. pins 28 andapertures 34) realignment with a more precise secondary datum (i.e. pins36 and apertures 24), and engagement of the mask assembly with ahold-down spring, remains the same. One can, for example, put bushingson the mask assembly which might engage with pins on the carrier, or onemight put bushings on the carrier which engage with pins on the maskassembly, or one might change the shape or location of the hold-downspring which activates the secondary alignment prior to engaging themagnet.

Additional advantages of this type of registration or alignment systemis that it is self-aligning and requires no expensive electro-opticalsensing to align the patterns. In operation, it provides operators witha direct view of the alignment correction by the amount that the maskappears shifted from having the pins in the center of the secondarydatums before engagement. This gives an early indication of problemswhich might be occurring with the primary datums. Finally, precisealignment by the system is extremely fast, occurring in less than half asecond, where other such methods require usually much longer than fiveseconds for operation.

While there have been shown and described what are at present consideredthe preferred embodiments of the present invention, it will obvious toone skilled in the art that various changes and modifications may bemade therein without departing from the scope of the invention asdefined by the appended claims.

What is claimed is:
 1. An apparatus for alignment of thin-film structurepatterns on a substrate formed with the use of an apertured mask in avacuum deposition system, said apparatus comprising:a mask frame; a maskassembly affixed to said mask frame, said mask assembly including saidapertured mask and mask alignment apertures disposed on either side ofsaid mask; a mask holder frame positioned adjacent said mask assemblyand affixed to said mask frame to form a mask holder assembly, said maskholder assembly having primary datum pins affixed thereto and protrudingfrom the side of said holder assembly opposite said mask assembly; and asubstrate carrier having a substrate supported therein, said substratecarrier being positioned adjacent to and in operative contact with saidmask holder assembly, said substrate carrier having primary datumapertures disposed about its periphery, said primary datum aperturesbeing located to engage with said primary datum pins of said mask holderassembly, said substrate carrier further having secondary datum pinsprotruding therefrom that engage with said mask alignment apertures ofsaid mask assembly.
 2. The apparatus according to claim 1 wherein saidmask frame includes means for aiding engagement of said mask assemblywith said secondary datum pins of said substrate carrier, saidengagement aiding means located substantially within and coplanar withsaid mask frame.
 3. The apparatus according to claim 2 wherein saidengagement aiding means includes spring plates mounted on and about saidmask frame, said spring plates being in operative contact with thesecondary datum pins that are in engagement with said mask alignmentapertures of said mask assembly, said spring plates being aligned withsaid mask alignment apertures.
 4. The apparatus according to claim 2wherein said apertured mask is structurally relieved from said maskassembly, which is rigidly attached within said mask holder assembly,such that said mask is capable of being in operative contact with saidsubstrate.
 5. The apparatus according to claim 4 wherein said maskalignment apertures of said mask assembly include a hole on one side ofsaid apertured mask and a slot on the other side of said apertured mask,said apertures engaging said secondary datum pins of said substratecarrier.
 6. The apparatus according to claim 4 wherein said apparatusfurther includes a magnet disposed adjacent and in operative contactwith said substrate carrier, said magnet disposed on the side of saidcarrier opposite said mask holder assembly.
 7. The apparatus accordingto claim 1 wherein said apertured mask is a mask for patterningelectrode structures.
 8. The apparatus according to claim 1 wherein saidapertured mask is a mask for patterning electrode pad contacts.
 9. Theapparatus according to claim 3 wherein said spring plates are pronged soas to be spring forks.